Upon removal of fixed appliances, many orthodontists prefer to place a tooth-positioning device that is made from plaster casts of the teeth at the end of treatment. The teeth in the cast are cut out and rearranged slightly in wax to the most ideal arrangement possible. A custom-made tooth positioner is flasked of rubber, silicone, vinyl, urethane, acrylic, or similar resilient material to exactly fit the teeth in this ideal arrangement. The positioner is placed before the bone sets around the teeth that have been moved by the fixed appliance. The patients wear the positioner to bed at night and clench into the positioner for four hours a day while the bone forms for an eight-week period, as an example of use. The positioner acts as a cast on a broken arm in that the teeth are held in the desired position and, moreover, it guides the teeth to the most ideal place by the resilient material actively moving each tooth as the teeth are clenched during the four-hour daytime wear period. The amount of movement is more or less limited by the mobility of each tooth in its periodontal membrane space at the time of placement. Many orthodontists take impressions with the fixed appliances still in place and remove them when the construction of the custom-made positioner is completed. Another alternative is to use an off-the-shelf stock preformed positioner to act as an intermediate form of retention until the custom-made one is ready.
The major disadvantage to this ideal approach is poor patient cooperation. Any removeable retention appliance has to be in use in the patients mouth if it is going to be successful. Positioners in their present day design are not very comfortable. Their excess bulk makes patients gag, choke, salavate excessively, and many patients experience breathing difficulties which are only partially helped by air holes. The result is that many patients do not wear positioners as prescribed and teeth are not retained well, let alone improved in position. When the orthodontist sees the completed result go back towards the original situation before treatment started, he and the patient are very unhappy and the positioner is blamed for failure. Most orthodontists do not use them because of failure due to lack of patient cooperation.
Present-day designs not only completely cover all exposed surfaces of the teeth but a significant amount of the gum tissue (gingiva) and underlying bone supporting the teeth. The design of the tooth positioner such as described in the original article by H. B. Kesling and as shown in U.S. Pat. Nos. 2,467,432 and 2,531,222, see FIG. 25, covers nearly three times the amount of the supporting gingiva and underlying bone as the labial and buccal surfaces of the teeth in the immediate area.